Solar mirrors are intended for equipping solar power plants, which, in a known manner, usually comprise a large number of reflectors, arrayed along the arcs of concentric circles, in order to reflect solar radiation to a boiler positioned at the top of a tower and located in the center of the array of reflectors. The boiler feeds steam to a turbine located at the base of the tower which in turn drives an electrical generator. Naturally it is necessary periodically to change the orientation of each of the reflectors in order for the reflected solar light to continue to be projected onto the boiler and, with a view to achieving this, the reflectors are mounted on adjustable bases, the position of which is automatically adjusted at regular intervals.
In order to prevent the luminous spot formed by each reflector on the receiver of the boiler from spreading beyond the limits of the receiver, the reflectors must be close in shape to a large radius spherical mirror.
Such mirrors must fulfill a certain number of requisites, among which are the following:
(a) they must be relatively inexpensive, in order for the solar power station to be competitive with traditional electrical generating plants; PA1 (b) they must be reliable, so as to curtail replacement, maintenance and adjustment costs; PA1 (c) they must keep a shape close to that of the ideal convergent mirror, in spite of deformation due to wind, heat and their own weight; and PA1 (d) they must be relatively lightweight, in order to simplify the design of the swivel base.
With a view to meeting these conditions, it has already been proposed by the Saint-Gobain Techniques Nouvelles corporation, in French patent application Ser. Nos. FR 76 07756 and published under No. FR 2 344 852 to build convergent mirrors comprising a frame which supports a plurality of reflecting elements or panels, at least one of which is appreciably cylindical and results from the deformation of a rectangular flat strip. Each of the panels are carried on the frame by means of elastomer edge strips which engage the long sides of the panels and also engage flanges formed integrally with the frame.
In constructing these mirrors, the rectangular reflecting strips are deformed at the work site by means of bending stresses applied along the entire length of the long sides of the strips when they are put into place on the supporting frame, while the short sides are left free during the bending of the long sides. More specifically, elastic deformation is imparted at the work site to a sectional member by the use of a template where the sectional member is destined to support the edge strip of a reflector panel and the sectional member thus deformed is fastened to the mirror frame.
In ordinary practice, mirrors of this type made in this manner comprise part of a rigid structure which can be directed in different directions with respect to a base anchored to the ground and where the rigid structure has a flat framework which supports T irons, arranged for example in vertical or horizontal lines, forming cambered sections which are brought onto the reference sphere by shaping. A shaping machine rolling on curved rails and equipped with a template arranged in a vertical plane makes it possible to place and fix each section on a beam in the desired position, after it has been cambered to the desired curvature.
This method makes it possible to rapidly assemble each mirror, but it requires a heavy, costly forming structure. This method also has the drawback that it can be utilized only at the site where the mirror is to be installed.
To remedy this drawback, solar mirrors have been proposed in which the reflector panels are supported by prefabricated cambered sections where the sections are assembled at the mirror assembly site prior to the reflector panels being positioned in place. Necessary adjustments to the sections are made without the necessity of using any heavy machines for shaping the sections at the site. Thus, in U.S. Pat. No. 4,226,506, there is disclosed a solar mirror comprising a rigid frame which can be moved with respect to a stationary base. The frame comprises joists formed by spaced parallel members provided with precambered sections which are curved to the curvature of the mirror and on which the long sides of rectangular reflector panels are connected by means of flexible fasteners while the short side of the panels remain free. In this mirror construction, the precambered sections are fastened by auxiliary T sections the flanges of which rest on the parallel members and the web of each of which has a longitudinal slot in which a web of the precambered sections is engaged and fastened.
By this construction it is possible to mount the auxiliary sections on the parallel members at the factory with the slot in a web being made straight by a suitable adjustment means. The precambered sections which are also T shaped are assembled in the slots while at the factory and shaped using a template. The resulting joist assemblies, including the parallel members and precambered sections are thus assembled along with the other structure making up the solar mirror at the mirror installation site.
The joists are assembled on girders of the frame by pins which are provided with adjustment means making it possible to adjust the distance between a girder and a member mounting a precambered section so that a radial adjustment is provided to assure that a panel surface is properly positioned with the mirror surface. More particularly, the members comprising the joists are mounted on the girders by assembly pins or gudgeons which extend perpendicular to the lengthwise direction of the girders and members. Each assembly pin is fixed with respect to a member and extends through a housing contained in a girder where the housing rests on a portion of the girder to support the weight of the reflector panels and frame. The pins engage a fastening element provided with articulated adjustment means by which the pins may be adjusted in an axial direction and which may accommodate pivoting of the member with respect to the girder.
It is an object of the present invention to provide a solar mirror of the general type as disclosed in U.S. Pat. No. 4,226,506 but which is less costly to manufacture and assemble and wherein the adjustment of the joists or parallel members with respect to a girder is simplified.